anybody have comparison pics between 8 1/4 and 8 3/4 drum backing plates??

Was the axle offset set-up for stock A body axles?
Which backing plates are you using?

As said above, the stock A body 8.75 backing plates will only work with stock A body offset axles. The brake backing plates for the A body 8.75 are unique.

Any large bolt pattern 1965 and up rear brakes will fit when swapped as a complete set-up. 7.25, 8.25, 8.75, dana.